1. Field of the Invention
This invention relates to a turbine vane with an enhanced profile.
2. Discussion of the Background
A conventional turbine vane comprises, as shown in FIG. 1, a mobile blade 1 in an annular section 2, a platform 3 confining the section 2 and a projection 4 inserted in a groove of a hub 5 belonging to the rotor. The blade 1, which is the essential part of the vane, may be broken down into stacked sections 6, located at increasing radial distances from the rotation axis of the machine and running, curving inwards, from a leading edge 7 to a trailing edge 8 of the flow of gases circulating in the section 2. The surfaces of the blade 1 consist of a blade face 9 and a suction face 10 each running between the leading and trailing edges 7 and 8, as illustrated in FIG. 2. The gases from the machine blow onto the blade face 9 and induce a rotational movement of the hub 5 and the vanes attached to it, to the right in the figures.
The profile of the blades 1 generally varies as illustrated in FIG. 3, the sections 6 being longer and curving less towards the platform 3, which is supposed to give a good flow and a satisfactory mechanical resistance.
However, the reason for the invention is the need to reduce the leakage current between the head 11 of blade 1 and the housing 12 around the section 2, between which a clearance must remain. These leakage currents run from the blade face 9 to the suction face 10 along the arrows 13 in FIG. 2; they produce an eddy downstream from the vane, which interferes with the gas flow.
The object of the present invention is to provide a selected solution which consists of deforming the sections 6 closer to the head 11 of the vane to reduce the leakage currents at this point. Some patents mention other deformations which may be applied to this part of the vane in relation to the typical profile in FIG. 3. In this manner, the international application WO 96 14469 describes a vane in which the blade is curved inwards towards the suction face in the vicinity of the head, resulting in an overhanging suction face. The purpose of this arrangement is to drive back the gases blown onto the suction face radially, to the rotation axis, to prevent them from reaching the blade head and moving to other side of the vane, to the blade face, by passing through the clearance adjacent to the housing 12. The pressure on the suction face increases close to the head 11, which reduces the difference in pressure between the two sides of the head 11 and the leakages over the head from the blade face to the suction face. It is also possible to reduce said leakage currents in this case in different ways and under different conditions, by bending or favoring the flow at the blade face of the vane in the tangential direction close to the head 11, which diverts it from the radial direction of its leakage.
The measures planned in this case consist of curving the trailing edge outwards at the tip end of the blade such that the blade sections closest to the end of the head are increasingly opened, i.e. pointing in the direction of the flow close to the trailing edge and, therefore, divert the flow less at this point.